Method of fabricating a phase-change memory

ABSTRACT

A phase-change memory comprises a bottom electrode formed on a substrate. A first isolation layer is formed on the bottom electrode. A top electrode is formed on the isolation layer. A first phase-change material is formed in the first isolation layer, wherein the top electrode and the bottom electrode are electrically connected via the first phase-change material. Since the phase-change material can have a diameter less than the resolution limit of the photolithography process, an operating current for a state conversion of the phase-change material pattern may be reduced so as to decrease a power dissipation of the phase-change memory device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a memory, and more particularly to aphase-change memory.

2. Description of the Related Art

Phase change memories are non-volatile, have high density, highcontrast, high cycling, and low power-consumption, thus, they are anindustry semiconductor of choice. Particularly, a phase-change memorywith high cell density capable of changing memory states with lowcurrent is desirable.

Phase-change materials may exhibit at least two different states,comprising amorphous and crystalline states. Phase-change materials maychange from the amorphous to the crystalline state, and back, inresponse to temperature changes. The states may be distinguished becausethe amorphous state generally exhibits higher resistivity than thecrystalline state. The amorphous state typically involves a moredisordered atomic structure, while the crystalline state is an orderedlattice. In general, chalcogenide materials have been widely used invarious optical recording media.

The resistance of the phase-change material varies according to whetherthe phase-change material is in a crystalline state or an amorphousstate. In detail, the phase-change material exhibits greater resistancewhen it is in an amorphous state than when it is in a crystalline state.Therefore, data can be read as logic “0” or logic “1” by detectingcurrent flowing through the phase-change memory when a predeterminedvoltage applied. That is, data can be stored in a digital form, logic“0” or logic “1”, without accumulation of electric charge.

U.S. Pat. No. 6,031,287 and U.S. Pat. No. 6,797,978 disclose horizontalphase-change memory with reduced phase-change material contact area andsufficient current density.

BRIEF SUMMARY OF THE INVENTION

In one embodiment of the invention, the phase-change memory comprises abottom electrode formed on a substrate. A first isolation layer isformed on the bottom electrode. A top electrode is formed on theisolation layer. A first phase-change material is formed in the firstisolation layer, wherein the top electrode and the bottom electrode areelectrically connected via the first phase-change material. Since thephase-change material can have a diameter less than the resolution limitof the photolithography process, an operating current for a stateconversion of the phase-change material pattern may be reduced so as todecrease a power dissipation of the phase-change memory device.

Methods of manufacturing phase-change memories are also provided. Anexemplary embodiment of a method comprises the following steps: forminga bottom electrode on a substrate; forming a first isolation layer onthe bottom electrode, wherein the first isolation layer comprises aplurality of first trenches exposing the bottom electrode, and the firsttrenches extend in a first extension direction; conformably forming afirst phase-change material on the first isolation layer and thesubstrate, wherein the first phase-change material covers the surface ofthe first trenches; forming a second isolation layer to fill the firsttrenches; subjecting the first isolation layer, the first phase-changematerial, and the second isolation layer to a planarization process;forming a plurality of first photoresist patterns extending in an secondextension direction parallel to the first extension direction, whereinthe first photoresist patterns cover the top surface of the firstphase-change material and exposing the top surface of the secondisolation layer formed into the first trenches; and etching the firstisolation layer, second isolation layer, first phase-change material,and bottom electrode with the first photoresist patterns as a maskexposing the substrate.

According to another exemplary embodiment of the invention, the methodof manufacturing phase-change memory comprises the following steps:forming a bottom electrode on a substrate; forming a first isolationlayer on the bottom electrode; patterning the first isolation layer soas to form a trench exposing the bottom electrode; conformably forming aphase-change material to cover the surface of the first isolation layerand the trench; etching the phase-change material to leave aphase-change material pillar adjacent to the sidewalls of the trenches;etching the bottom electrode exposed in the trenches to expose thesubstrate; and forming a second isolation layer to fill the trench.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIGS. 1-8 are cross sections of showing a method of fabricating aphase-change memory according to an embodiment of the invention.

FIGS. 9-11B are cross sections of showing a method of fabricating aphase-change memory according to another embodiment of the invention.

FIGS. 12-15 are cross sections of showing a method of fabricating athree-dimensional phase-change memory according to yet anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is the best-contemplated mode of carrying outthe invention. This description is made for the purpose of illustratingthe general principles of the invention and should not be taken in alimiting sense. The scope of the invention is best determined byreference to the appended claims.

Referring to FIG. 1, a substrate 101 is provided, wherein the substrate101 can be a semiconductor substrate. Next, a bottom electrode 103 isformed on the substrate 101, wherein the bottom electrode 103 can beTiN, TaN, or TiW, and formed by CVD or sputtering. Next, an isolationlayer 105 is formed on the bottom electrode 103. The isolation layer 105is preferably thicker than the bottom electrode 103. For example, thematerial of the isolation layer 105 may be borophosphosilicate glass(BPSG), silicon oxide, or silicon nitride, serving as the etching-stopof a subsequent chemical mechanical polishing (CMP) process.

Next, referring to FIG. 2, the isolation layer is patterned byphotolithography processes to form a plurality of trenches 201 exposingthe bottom electrode 103. Note that the distance between thephase-change materials of memories of the invention depends on the widthof the trenches 201. The trench 201 extends in a first extensiondirection.

Next, a phase-change material 203 is conformably formed on the isolationlayer 105 and the bottom electrode 103, completely covering thesidewalls and the bottom of the trenches 201, wherein the phase-changematerial 203 covers the top surface of the bottom electrode 103 withinthe trenches 201. The phase-change material 203 can be a chalcogenidematerial or comprise In, Ge, Sb, Te or combinations thereof, such asGeSbTe or InGeSbTe. Particularly, the thickness of the phase-changematerial 203 can be 20 nm to 100 nm, preferably 50 nm.

Referring to FIG. 3, an isolation material 305 is filled into thetrenches 201 and planarized by a planarization process, such as CMP,leaving coplanar top surfaces of the isolation layer 105, phase-changematerial 203, and isolation layer 305. For example, the material of theisolation layer 305 can be borophosphosilicate glass (BPSG), siliconoxide, or silicon nitride. Preferably, the material of the isolationlayer 305 and the isolation layer 105 is substantially the same. Theetching back process may replace the planarization process.

Next, referring to FIG. 4, a photoresist layer is formed on theisolation layer 105, phase-change material 203, and isolation layer 305and patterned to form a plurality of photoresist patterns 401 extendingin a second extension direction parallel to the first direction. Thephotoresist patterns 401 cover the entire top surface of thephase-change material 203 and partially cover the top surface of theisolation layer 305 and isolation layer 105. The distance between thememories depends on the distance between the photoresist patterns 401.

The isolation layer 105, isolation layer 305, phase-change material 203,and bottom electrode 103 are etched with the photoresist patterns as amask exposing the substrate 101, completing the structure 501 as shownin FIG. 5. It should be noted that the phase-change material 203 isformed between the isolation layer 105 and isolation layer 305 and isL-shaped or ┘-shaped and electrically connects to the bottom electrode103.

Referring to FIG. 6, an isolation layer 605 is filled into the openingsbetween the stacked structures 501. For example, the material of theisolation layer 605 can be borophosphosilicate glass (BPSG), siliconoxide, or silicon nitride. Preferably, the material of the isolationlayer 605 and the isolation layer 105 is substantially the same. Theisolation layer 105, phase-change material 203, isolation layer 305, andisolation layer 605 are planarized by a planarization process, such aschemical mechanical polishing, resulting in coplanar top surfaces of theisolation layer 105, phase-change material 203, isolation layer 305, andisolation layer 605.

Still referring to FIG. 6, a photoresist layer is formed on theisolation layer 105, phase-change material 203, isolation layer 305 andisolation layer 605, and patterned to form a plurality of photoresistpatterns 601 extending in a third extension direction perpendicular tothe first direction. FIG. 7 shows the top-view of FIG. 6. The width W ofthe photoresist patterns 601 is preferably the same as the resolutionlimit of photolithography process, resulting in reducing the top area ofthe phase-change material and increasing the current density of thephase-change memory.

The isolation layer 105, isolation layer 305, isolation layer 605,phase-change material 203, and bottom electrode 103 are etched with thephotoresist patterns 601 as a mask exposing the substrate 101. FIG. 8shows the top-view of the described structure.

In another embodiment, the order of forming the photoresist patterns 401and the photoresist patterns 601 can be changed. Referring to FIG. 3,after performing the first planarization, the photoresist patternsextending in a extension direction perpendicular to the first directioncan be formed on the isolation layer 105, phase-change material 203, andisolation layer 305. After etching and deposition of the isolation, thephotoresist patterns extending in a extension direction parallel to thefirst direction are then formed.

A method of fabricating a phase-change memory is also provided.Referring to FIG. 9, a conducting layer 903 and an isolation layer 905are formed on a substrate 901.

Suitable materials for the conducting layer 903 can be TiN, TaN, or TiW,serving as the bottom electrode of the invention. For example, thematerial of the isolation layer 905 may be borophosphosilicate glass(BPSG), silicon oxide, or silicon nitride. Next, the isolation layer 905is patterned to form a plurality of trenches 909 exposing the conductinglayer 903

A phase-change material 907 is conformably formed on the isolation layer905 and the conducting layer 903, completely covering the sidewalls andthe bottom of the trenches 909, wherein the phase-change material 907cover the top surface of the conducting layer 903 within the trenches909. The phase-change material 907 can be chalcogenide material orcomprise In, Ge, Sb, Te or combinations thereof, such as GeSbTe orInGeSbTe. Particularly, the thickness of the phase-change material 907can be 20 nm to 100 nm, preferably 50 nm.

Referring to FIG. 10, the phase-change material 907 is etched by ananisotropic etching to remain a phase-change material pillar adjacent tothe sidewalls of the trenches. Next, the conducting layer 903 within thetrenches 909 is etched to form openings 910 exposing the substrate 901.

Next, referring to FIG. 11A, an isolation layer 911 is formed to fillthe openings 910, and planarized by a planarization process, such aschemical mechanical polishing, leaving coplanar top surfaces of theisolation layer 905, phase-change material 907, and isolation layer 911.For example, the material of the isolation layer 911 may beborophosphosilicate glass (BPSG), silicon oxide, or silicon nitride.Referring to FIG. 11B, the described structure is subjected to theprocess as disclosed in FIGS. 6˜8, thus, fabrication of the phase-changememory is complete. Particularly, the phase-change material pillar isformed between the isolation layer 905, and isolation layer 911, and theprofile of the phase-change material pillar is I-shaped.

In some embodiments of the method for fabricating a three-dimensionalphase-change memory comprises: after planarization process as disclosedin FIG. 3, an isolation layer 121 is formed on the isolation layer 105,phase-change material 203, and isolation layer 305. For example, thematerial of the isolation layer 121 can be borophosphosilicate glass(BPSG), silicon oxide, or silicon nitride. Next, the isolation layer 121is patterned to form a plurality of trenches 123, wherein the trenches123 are parallel to and directly over the trenches 201. Particularly,the width of the trenches 123 can be the same as the trenches 201, andthe trenches 123 and trench 201 extend to a first extension direction.

A phase-change material 125 is formed conformably on the isolation layer121 and the trenches 123, wherein the phase-change material 125 coverthe sidewalls and the bottom of the trenches 125. An isolation layer 131is filled into the trenches 123. For example, the material of theisolation layer 131 can be borophosphosilicate glass (BPSG), siliconoxide, or silicon nitride.

The isolation layer 121, phase-change material 125, and isolation layer131 are planarized by a planarization process, such as chemicalmechanical polishing, leaving coplanar top surfaces of the isolationlayer 121, phase-change material 125, and isolation layer 131. Theetching back process may replace the planarization process.

Referring to FIG. 13, after planarization, a photoresist layer is formedon the isolation layer 121, phase-change material 125, and isolationlayer 131, and patterned to form a plurality of photoresist patterns 133extending in a second extension direction parallel to the firstextension direction.

The photoresist patterns 133 cover the entire top surface of thephase-change material 203 and phase-change material 125 adjacent to thesidewalls of the trenches 201 and trenches 123 and cover a partial topsurface of the isolation layer 131 and isolation layer 121.

Next, referring to FIG. 14, the isolation layer 121, isolation layer131, phase-change material 203, phase-change material 125, isolationlayer 105, isolation layer 301 and bottom electrode 103 are etched withthe photoresist patterns 133 as a mask exposing the substrate 101,forming a plurality of stacked structures 141. The phase-change material125 is formed between the isolation layer 131 and isolation layer 121,and phase-change material 203 is formed between the isolation layer 301and isolation layer 105. The phase-change material 125 and phase-changematerial 203 are L-shaped or ┘-shaped, electrically connecting eachother. Further, a conducting layer (not shown), such as TiN, TaN, orTiW, can be formed between the phase-change material 125 andphase-change material 203, serving as an electrode. Preferably, sincethe phase-change material 125 and phase-change material 203 comprisedifferent materials, data can be read in logic “10”, logic “01”, logic“00”, or logic “11” by detecting current flowing through thephase-change memory when a predetermined voltage applied, therebyincreasing the memory density thereof.

Next, referring to FIG. 15, an isolation layer 151 is formed on thesubstrate to fill the space between the stacked structures 141, andplanarized by a planarization process, such as chemical mechanicalpolishing, leaving coplanar top surfaces of the isolation layer 121,isolation layer 131, isolation layer 151, and isolation layer 125. Forexample, the material of the isolation layer 151 can beborophosphosilicate glass (BPSG), silicon oxide, or silicon nitride.

Next, a photoresist layer is formed on the above structure to form aplurality of photoresist patterns 153 extending in a third extensiondirection perpendicular to the first direction. The top-view of theaforementioned structure is the same as the FIG. 7.

The width of the photoresist patterns 153 is preferably the same as theresolution limit of photolithography process, resulting in reducing thetop area of the phase-change material and increasing the current densityof the phase-change memory.

The isolation layer 121, isolation layer 131, isolation layer 105,isolation layer 301, phase-change material 125, phase-change material203, and bottom electrode 103 are etched with the photoresist patterns153 as a mask exposing the substrate 101. FIG. 8 shows the top-view ofthe above structure.

After removing the photoresist patterns 153, a conducting layer isformed on the top surface of the phase-change material 125 forelectrical connection thereto. Next, the conducting layer is etched toform a plurality of top electrodes extending in a fourth extensiondirection perpendicular to the first extension direction.

Accordingly, the contact area between the phase-change material and topelectrode depends on the deposition thickness of the phase-changematerial and the width of the photoresist patterns. Therefore, thephase-change material can have a diameter less than the resolution limitof the photolithography process. As a result, an operating current for astate conversion of the phase-change material pattern may be reduced soas to decrease a power dissipation of the phase-change memory device. Inaddition, because the operating current decreases, sizes of otherdiscrete devices (e.g., MOS transistor) of the phase-change memorydevice may also be decreased. Therefore, the phase-change memory devicemay be suitable for high integration.

Moreover, in an embodiment of the invention, the phase-change memorieshave four kinds of logic single, thereby increasing the memory densitythereof.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

1-24. (canceled)
 25. A method of fabricating a phase-change memory,comprising: forming a bottom electrode on a substrate; forming a firstisolation layer on the bottom electrode; patterning the first isolationlayer so as to form a trench exposing the bottom electrode; conformablyforming a phase-change material to cover the surface of the firstisolation layer and the trench; etching the phase-change material toremain a phase-change material pillar adjacent to the sidewalls of thetrenches; etching the bottom electrode exposed in the trenches to exposethe substrate; and forming a second isolation layer to fill the trench.26. The method as claimed in claim 25, further comprising forming a topelectrode on the phase-change material.
 27. The method as claimed inclaim 25, wherein the profile of the phase-change material is I-shaped.28. The method as claimed in claim 25, wherein the phase-change materialcomprises chalcogenide material.
 29. The method as claimed in claim 25,wherein the first isolation layer comprises borophosphosilicate glass(BPSG), silicon oxide, or silicon nitride.
 30. The method as claimed inclaim 25, wherein the first isolation layer and the second isolationlayer comprise substantially the same material.